If PTET was not paid by 12/31/21 it will NOT be deductible in 2021, cash OR accrual basis.  There's debate whether it is deductible on 2021, or if it's a 'deposit'.  The IRS specific guidance is MIA; disclosure is suggested.

I have one client that his credit IS limited by TMT, but the disallowed amount is available to carryforward for 5 years. It isn't lost.  And we may not make the election for 2022 given the large carryover.   Having the entity pay the PTET by 12/31/21 gave him +/- $ 350,000 credit on his F 540.  And saved almost $ 200,000 on his Fed tax bill.

My point is - run the numbers, discuss with your client. Compute the cash flow.  One answer doesn't fit all.